Julio San Román

Self-curing membranes of chitosan/PAA IPNs obtained by radical polymerization: preparation, characterization and interpolymer complexation

Chitosan/polyacrylic acid I PNs were prepared by radical polymerization of acrylic acid, AA, activated at low temperature, in an aqueous/alcoholic chitosan dispersion. AA monomer to polymer conversion and membrane compositions were determined by elemental analysis and FTIR. Evidences of interpolyelectrolite complex formation were found from the FTIR spectra as well. The gravimetric measurements and the elemental analysis after some exhaustive PAA extraction support the existence of some PAA grafting on the reactive amine group of the chitosan. Swelling degree of the membranes is highly dependent on pH and composition, showing a higher swelling in membranes richer in AA and increased pH due to the breaking of interpolyelectrolite salt bonds.

A kinetic study of the thermal degradation of chitosan and a mercaptan derivative of chitosan

Abstract The thermal degradation behaviour of chitosan and N -(2-hydroxy-3-mercaptopropyl)-chitosan (HMPC) has been studied by means of dynamic thermogravimetric analysis (TGA) in the range 30–600°C. Dynamic experiments showed that thermal decomposition of both products proceeds in four steps. The apparent activation energy values for each degradation step were obtained following the procedure of Broido. The first decomposition stage of both products was also studied by isothermal TGA and it was found that the apparent activation energy varies with degree of conversion, which is a manifestation of the complexity of this decomposition stage for both polysaccharides. In the pyrolysis-mass spectra of chitosan and HMPC the lower stability of the latter is apparent, since it exhibits peaks at m z 34, 47 and 76, not observed for chitosan, due to evolution of H 2 S and CH 3 S and C 2 H 4 OS fragments, respectively. The IR spectra of residual chitosan chars from isothermal pyrolysis gave an indication of degradation of the ring together with dehydration over the whole temperature interval studied. In the IR spectra of HMPC pyrolysis residues no appreciable degradation of the glycopyranosic ring was observed up to 200°C; at higher temperatures, the behaviour is similar to that of chitosan.

New partially degradable and bioactive acrylic bone cements based on starch blends and ceramic fillers

This work reports the development of new partially biodegradable acrylic bone cements based on corn starch/cellulose acetate blends (SCA), prepared by the free radical polymerization of methyl methacrylate and acrylic acid at low temperature. Amounts of biocompatible, osteoconductive and osteophilic mineral component such as hydroxylapatite (sintered and non-sintered), were incorporated in different percentages to confer a bone-bonding character to the bone cements in this type of applications. All cement formulations were characterized by 1H NMR spectroscopy. Curing parameters and mechanical properties were determined finding formulations which complete the ASTM legislation. Hydration degree, degradation studies, as well as bioactivity tests were performed in all prepared formulations. The developed systems show a range of properties that might allow for their application as self-curing bone cements, exhibiting several advantages with respect to other commercially available bone cements.

Water sorption of flexible networks based on 2- hydroxyethyl methacrylate-triethylenglycol dimethacrylate copolymers

Abstract Cross-linked films of copolymer of 2-hydroxyethyl methacrylate (HEMA) and triethylenglycol dimethacrylate (TEGDMA) were prepared by free radical polymerization initiated at 60°C. The swelling behaviour of films prepared with 2, 5 and 10 mol% of TEGDMA was followed gravimetrically and the diffusion coefficients were determined according to the Fickian law at several temperatures in the interval 25–50°C. The apparent activation energy was independent of the composition of the networks, giving a value of 15.5 kJ mol−1 which corresponds to a typical diffusion process. The freezing point, the enthalpy of fusion and the amount of non-freezable water were determined by differential scanning calorimetry (DSC) on hydrated samples with different hydration degree. There is a critical hydration interval (W = 20–30 wt%) in which it is possible to distinguish the different states of water in the cross-linked hydrogel. The variation of the enthalpy ΔHf with the hydration degree gives a maximum amount of non-freezable water of about 23 wt%, independent of the TEGDMA content of copolymer systems.

Effect of magnesium content on the in vitro bioactivity of CaO-MgO-SiO2-P2O5 sol-gel glasses

Three glasses in the system CaO-MgO-SiO 2 -P 2 O 5 , with high silica content (80 mol% SiO 2 ) and 0, 3 and 7 mol% of MgO, respectively, have been prepared by the sol-gel method. The in vitro bioactivity of pellets, prepared by compacting the glass powders, was assessed by determining the changes in surface morphology and composition after soaking in a simulated body fluid (SBF) for up to 14 days at 37 °C. Formation of a calcium phosphate rich layer on the glasses surface was followed by scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Three effects of MgO in the glass upon the newly formed layer were detected: (i) it slows down the rate of formation of the layer, (ii) it increases the thickness of the layer and (iii) a whitlockite-like phase appeared together with the apatite-like phase formed on the surface of bioactive materials when exposed to physiological solutions.

Interpolymer complexes of chitosan and polymethacrylic derivatives of salicylic acid : preparation, characterization and modification by thermal treatment

Macromolecular interpolymer complexes were prepared by blending concentrated equimolar solutions of chitosan and poly(4-N-methacrylamidobenzoic acid) and evaporation of the solvents. The products obtained presented the structure of interpolymer complexes as indicated by FTIR spectroscopy. The thermal treatment of the solid products at 120°C gives rise to a partial dehydration together with the formation of covalent amide bonds between both polymeric components. The sorption behaviour of the systems is analysed on the basis of the structure of the macromolecular systems and a consideration of Fickian behaviour for highly hydrophilic materials. The diffusion coefficients determined are dependent on the thermal treatment applied to the interpolymer complexes.

New physically adsorbed polymer coating for reproducible separations of basic and acidic proteins by capillary electrophoresis

In this work, a new physically adsorbed coating for capillary electrophoresis (CE) is presented. The coating is based on a N,N-dimethylacrylamide-ethylpyrrolidine methacrylate (DMA-EPyM) copolymer synthesized in our laboratory. The capillary coating is simple and easy to obtain as only requires flushing the capillary with a polymer aqueous solution for 2 min. It is shown that by using these coated capillaries the electrostatic adsorption of a group of basic proteins onto the capillary wall is significantly reduced allowing their analysis by CE. Moreover, the DMA-EPyM coating provides reproducible separations of the basic proteins with RSD values for migration times lower than 0.75% for the same day (n = 5) and lower than 3.90% for three different days (n = 15). Interestingly, the electrical charge of the coated capillary wall can be modulated by varying the pH of the running buffer which makes possible the analysis of basic and acidic proteins in the same capillary. The usefulness of this coating is further demonstrated via the reproducible separation of whey (i.e. acidic) proteins from raw milk. The coating protocol should be compatible with both CE in microchips and CE-MS of different types of proteins.

Crosslinkable PEO-PPO-PEO-based reverse thermo-responsive gels as potentially injectable materials

This paper describes the functionalization and crosslinking of PluronicRTM derivatives in aqueous solution at 37° C. Pluronic dimethacrylate was obtained by reacting native PEO-PPO-PEO triblocks with methacryloyl chloride and then crosslinking them by free radical polymerization at 37° C, using a redox system. The resulting gel and its rheological behavior were characterized by different techniques. The swelling study of the crosslinked polymer was indicative of its reverse thermo-responsive behavior, as illustrated by the almost 800% water uptake of the polymer at 37° C, as opposed to the 1600% attained by the polymer at 25° C. As expected, while the Pluronic dimethacrylate gel displayed an E c value of 142.5 ± 29.7 kPa at 37° C, the crosslinked system attained a Youngs modulus three times higher: 415.2 ± 45.7 kPa. Finally, the environmental SEM analysis revealed the porous microstructure of the crosslinked gels.

Hydrophilic hybrid IPNs of segmented polyurethanes and copolymers of vinylpyrrolidone for applications in medicine

The preparation and biocompatibility properties of thermoplastic apparent interpenetrating polymer networks (T-IPNs) of a segmented polyurethaneurea, Biospan (BS), and vinylpyrrolidone-dimethylacrylamide (VP-DMAm) copolymers, are described. The biological interaction between the obtained materials and blood was studied by in vitro methods. The addition of the VP-DMAm copolymers to form T-IPNs with BS substantially increased the equilibrium water uptake and water diffusion coefficients. Investigation of the proteins adsorption, platelet adhesion, thrombus formation and factor XII activation is presented. Investigations of the proteins adsorption of the BS/VP-DMAm T-IPNs surfaces show that the segmented polyurethane (BS) containing VP-DMAm copolymers with higher VP content adsorb more albumin than fibrinogen and gamma-globulin. The platelets adhesion, thrombus formation and factor XII activation are effectively suppressed with respect to the segmented polyurethane when VP-DMAm copolymers with high VP contents are incorporated into BS as T-IPNs.

Biochemical Evidence That phaZ Gene Encodes a Specific Intracellular Medium Chain Length Polyhydroxyalkanoate Depolymerase in Pseudomonas putida KT2442 CHARACTERIZATION OF A PARADIGMATIC ENZYME

Polyhydroxyalkanoates (PHAs) can be catabolized by many microorganisms using intra- or extracellular PHA depolymerases. Most of our current knowledge of these intracellular enzyme-coding genes comes from the analysis of short chain length PHA depolymerases, whereas medium chain length PHA (mcl-PHA) intracellular depolymerization systems still remained to be characterized. The phaZ gene of some Pseudomonas putida strains has been identified only by mutagenesis and complementation techniques as putative intracellular mcl-PHA depolymerase. However, none of their corresponding encoded PhaZ enzymes have been characterized in depth. In this study the PhaZ depolymerase from P. putida KT2442 has been purified and biochemically characterized after its overexpression in Escherichia coli. To facilitate these studies we have developed a new and very sensitive radioactive method for detecting PHA hydrolysis in vitro. We have demonstrated that PhaZ is an intracellular depolymerase that is located in PHA granules and that hydrolyzes specifically mcl-PHAs containing aliphatic and aromatic monomers. The enzyme behaves as a serine hydrolase that is inhibited by phenylmethylsulfonyl fluoride. We have modeled the three-dimensional structure of PhaZ complexed with a 3-hydroxyoctanoate dimer. Using this model, we found that the enzyme appears to be built up from a coreα/β hydrolase-type domain capped with a lid structure with an active site containing a catalytic triad buried near the connection between domains. All these data constitute the first biochemical characterization of PhaZ and allow us to propose this enzyme as the paradigmatic representative of intracellular endo/exo-mcl-PHA depolymerases.